This invention relates to improvements in the manufacturing of relief printing plates made of photo-sensitive polymeric material, which offer several advantages over conventional systems, these advantages being mainly cost-related.
As it is well known, the procedure for manufacturing of this conventional type of printing plate is as follows: a suitable photopolymeric material, i.e. a photo-sensitive viscous resin, and a photographic negative which is placed in an insolating machine must be used. The resin is poured on the negative and the whole is covered with a transparent polyester sheet. Then, ultraviolet light which is projected from both sides penetrates through this base and through the negative transparent portions (which correspond to letters or designs for the printing plate), the resin that has received the radiations becomes hardened and follows the letter or design edges. This action causes the final base to be formed by the polyester sheet and a hardened resin layer, from which the reliefs determining the letters or designs protrude. Manufacturing ends by washing with water and a neutral detergent at 40.degree. C. to remove the remaining viscous resin, and then a second exposure to ultraviolet radiation is performed to harden the letters or design side walls. Afterwards, the printing plate is dried, becoming ready for its use.
This usual procedure has the disadvantage that not all the viscous resin among the hardened portions is recovered, since some amount of such resin constitutes the hardened layer which, together with the polyester sheet, determines the base of the printing plate.